You've probably tried the standard Nordic curl before. It looks something like this:
It's a good exercise, but it tends to inflict some knee discomfort because the knee-joint angle opens when the body descends. I've always suspected it's because of the stress they inflict on the posterior cruciate ligament.
Instead, try this variation:
Nordic Curl Hip Hinge
What you'll do is change the emphasis to keep an isometric hold at the knee joint while incorporating a hinge movement at the hip joint. This makes the hamstrings work hard while reducing posterior ligament stress.
Pay attention to detail. An easy default is letting the hips drop back too far when hinging (letting the butt "sit" toward the heels). Don't let this happen. Start your set by leaning forward 2 or 3 inches to place the tension on the hamstrings throughout.
Your tall position shouldn't be free of tension. In other words, if there was nothing blocking your feet, you'd likely fall forward. Squeeze the glutes through the hinge pattern and keep moving slowly.
A 25-pound plate should be all you need if you weigh over 200. For even bigger guys, bodyweight is just fine. Focus on sets of 10.